sedimentary
Petoskey Stone
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-4 (Mohs scale), Color: Gray to brown when dry, pattern visible when wet. Luster: Dull to earthy (unpolished) or vitreous (polished). Structure: Hexagonal colonial coral patterns. Specific Gravity: 2.7.
- Color
- Gray to brown when dry, pattern visible when wet
- Luster
- Dull to earthy (unpolished) or vitreous (polished)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Gray to brown when dry, pattern visible when wet. Luster: Dull to earthy (unpolished) or vitreous (polished). Structure: Hexagonal colonial coral patterns. Specific Gravity: 2.7.
Formation & geological history
Formed from fossilized colonial rugose corals from the Devonian period, approximately 350-400 million years ago. These corals lived in warm, shallow seas that once covered Michigan.
Uses & applications
Predominantly used for jewelry, decorative carvings, and as a popular collector's item. In the past, it was used for local construction/fill before its significance was realized.
Geological facts
It is the official state stone of Michigan. The name 'Petoskey' comes from an Ottawa Indian Chief, Pet-O-Sega. The 'eyes' in the stone are actually the individual coral polyps (corallites).
Field identification & locations
Identify by wetting the stone to reveal the unique hexagonal 'honeycomb' pattern. Commonly found along the shores of Lake Michigan and Lake Huron, particularly in the Petoskey area.
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